Electroless deposition of nickel-phosphorus based alloys



United States Patent Oflice U.S. Cl. 29-194 Claims ABSTRACT OF THEDISCLOSURE Articles of manufacture made from a basis metal having anelectrolessly deposited nickel-phosphorus based alloy coating thereon,the alloy containing from more than 1% to about 45% of an element whichis codeposited with the alloy, the element being tungsten, rhenium,berylluim, rhodium, palladium, platinum, tin, zinc, molybdenum or gold.The nickel predominates the phosphorus in quantity.

The invention described herein may be manufactured and used by or forthe Government for governmental purposes without the payment to one ofany royalty thereon.

This invention is a divisional application of my copending applicationSer. No. 407,941, filed Oct. 30, 1964, for Electroless Deposition ofNickel-Phosphorus Based Alloys, now abandoned and relates to electrolessdeposition and more particularly concerns the electroless de position ofnickel-phosphorus alloys containing tungsten, zinc, tin, rhenium andmolybdenum.

Nickel coatings have long been used for improving the appearance ofsteel products and yet protecting the basis metal from harmful orcorrosive attacks. Until recently, nickel plating was accomplished by anelectrodeposition process which suffered essentially in the poorthrowing power of the electrodeposited nickel making it difiicult toachieve uniformly of coating on irregularly shaped objects.

In the prior art, a chemical nickel plating process was developed basedon the reduction of nickel salts by hypophosphite, and is representedapproximately by the following reaction:

catalytic Ni++ 2H PO2' 21120 Ni ZHPO 411+ H2 sur on The electrolessdeposition of nickel, or more correctly, nickel-phosphorus alloys,occurs wherever the basis metal is in contact with the electrolessplating solution and provides excellent deposition uniformity. I haveplated numerous small, intricately shaped steel components, such, forexample, as timing mechanisms, very successfully, with the electrolessprocess, whereas the electrodeposition process was ineffective inplating such mechanisms. Similarly, the interiors of long, narrow tubescan readily be plated with the elecroless nickel process whereas it isvirtually an impossible task to be accomplished by standardelectrodeposition methods. Further, the hardness of electrolessdeposited nickel is greater than that of electrodeposited nickel and canbe further increased by additional heat treatment. A further interestingfeature of electroless deposited nickel resides in the fact that it canbe readily applied directly over properly activated non-conductors.However, the prior art electroless technique is restrictive in that varyfew metals can be deposited thereby. In addition, there are manyapplications wherein improved tarnish resistance,

3,485,597 Patented Dec. 23, 1969 to acid attack, ductlity, corrosionprotection of a basis metal, high temperature oxidation resistanc andwear resistance would be desirable.

It is therefore a principal object of this invention to provide new anduseful electroless nickel-phosphorus based alloys containing othermetals.

Another object of th invention is to provide bath solutions for theelectroless deposition of nickel-phosphorus alloys containing othermetals.

Other and further objects of the invention will be apparent to thoseskilled in the art upon study of this disclosure.

Briefly, and in accordance with my invention, I have discovered thattarnish-resistant and/or corrosion resistant alloys can be successfullyelectroless plated onto the basis metals normally employed inelectroless nickel deposition.

More specifically, I have found that when sodium tungsten is added tothe prior art acid-citrate electroless nickel solution bath and the pHof the bath is raised above about 7, substantial tungsten content isdetected in deposits. In order to prevent the precipitation of nickelsalts at higher pH values, the concentration of the nickel salts isdecreased to about 20% of the usual concentration (35 g./l. of NiSO -6HO) and the remaining replaced by an atomic equivalent of tungstenobtained from sodium tungstate.

In Table I it will be seen that I have successfully electroless platednickel-phosphorus alloys containing tungsten from an unammoniatedalkaline citrate bath solution.

TABLE L-NICKEL-PHOSPHORUS ALLOY OF TUNGSTEN FROM UNAMMONIATED ALKALINECITRATE BATH The effective range of pH is between 7 and 10 although a pHof '8.2 is preferred. The bath temperature range is between about to C.with 98 C. being most desirable. The amount of tungsten in theelectroless deposit is about 13% with the balance being about 94% nickeland 6% phosphorus when using the preferred bath of Table I above.

' Sirninlarly, I have found that tin, zinc, rhenium, beryllium andrhodium may be electroless deposited with the nickel-phosphorus when theappropriate metal salt is used in place of sodium tungstate in theexampl of Table I above. See Table II.

NOTE.-A11 bath solutions were operated at 98 C. and pH=8.2.

These alloys however require that the bath solution be stabilizedagainst decomposition such as by the addition of about 0.2 ml./l. of asolution of 10 g./l. of mercaptobenzothiazole in 2 N NaOH.

In addition, I have found that a number of metals, including rhenium,zinc, molybdenum and tin, can be codeposited with nickel-phosphorususing an ammoniated alkaline citrate bath. See the examples of TableIII,

TABLE III Bath Composition Content of Effective Preferred Deposit fromPreferred Bath Composition D Tungsten as NazWO4'2HzO 20-80 moi percent60 moi percent 12% Tungsten.

Rhenium as KReO4. Zinc as ZnSO4-7Hz0.

10-40 moi percent.

1-20 moi percent 4 moi percent 45% Rhonium.

. 20 moi percent 8% Zinc.

Tin as NagSn -3HzO 5-20 mol percent. moi percent. 2% Till. Molybdenum asNa MoO 0.1-0.4 moi percen 0.2 moi percent- 6% Molybdenum. Palladium asPdClz 0. 1-1. 0 moi percent. 0.7 moi percent. 5% Palladium. Platinum asHPtCli 3H2O... 0.1-1.0 moi percent. 0. 4. mol percent 1% Platinum. Goldas HAuO14-3H2O 0.1-1.0 moi percent 0. 4 moi percent. 1% Gold.

Balance being Ni-i-P.

N orE.-Xmetal salt which is the source of metal codcpositing with Ni.

The preferred pH for the electroless plating from the ammoniatedalkaline citrate bath is 9.0 at a bath temperature of 98 C. Theeffective pH and temperature ranges will be about 8 to 10 and 90 to 100C. respectively. The pH is maintained by periodic additions of NH OH.Further, any combination of tungsten, tin, rhenium, zinc and molybdenummay be codeposited electrolessly with nickel-phosphorus. For example,nickel-phosphorus-rhenium-tungsten may be electroless deposited fromboth an unammoniated and an ammoniated alkaline citrate bath.

Salt Spray Corrosion tests were performed on steel panels coated with0.3 .mil of some of the deposits shown in Tables I and III. Mynickel-phosphorus-tin and nickelphosphorus-rhenium deposits exhibitedsuperior corrosion protection of the steel substrate as compared to thestandard electroless nickel deposit. My nickel-phosphorustin andparticularly my nickel-phosphorus-tungsten deposits provided superiortarnish resistance qualities.

Acid resistance tests performed on the aforementioned panels revealedthat my nickel-phosphorus-tungsten deposit has superior reistance to 50%nitric acid attack over conventional electroless-nickel coated panels.

The nickel-phosphorus-zinc coating was found to be 100 miilivolts moreactive in potential than conventional electroless nickel deposits. Thisproperty is useful for sacrificial protection of certain metals.

It is apparent that m the foregoing description of my invention, newbath compositions are described for yielding electroless depositedalloys which are useful for providing superior corrosion protectiveproperties to a basis metal and for imparting excellent tarnishresistant properties thereto.

I claim:

1. An article of manufacture comprising a basis metal structure havingan electroless deposited coating thereon, said coating consistingessentially of an alloy of nickel, phosphorus and at least one elementselected from the group consisting of tungten, molybdenum, rhenium,beryllium, rhodium, palladium, and platinum, said alloy beingcharacterized as a nickel-phosphorus based alloy wherein nickel ispresent in major proportions and phosphorus is present in minorproportions, and wherein said element is present in an amount rangingbetween greater than 1% to about 2. An article according to claim 1 mentcomprises tungsten.

3. An article according to ment comprises molybdenum.

4. An article according to ment comprises rhenium.

5. An article according to ment comprises beryllium.

6. An article according to ment comprises rhodium.

7. An article according to ment comprises palladium.

8. An article according to ment comprises platinum.

9. An article according to claim 2 wherein said tungsten comprises atleast 13% by weight of said coating.

10. An article according to claim 4 wherein said rhenium comprises atleast 45% by weight of said coating.

wherein said eleclaim 1 wherein said eleclaim 1 wherein said eleclaim 1wherein said eleclaim 1 wherein said eleclaim 1 wherein said ele claim 1wherein said ele- References Cited UNITED STATES PATENTS 2,828,2273/1958 Eisenberg 117-130 2,995,473 8/1961 Levi 117-130 X 3,077,2852/1963 Budininkas 29-l96.6 X 3,178,311 4/1965 Cann 117-130 X 3,202,5388/1965 Beynon 117-130 X 3,234,031 2/1966 Z'rrngiebl et al. 106-13,370,979 2/1968 Schmeckenbecher 117-130 X L. DEWAYNE RUTLEDGE, PrimaryExaminer E. L. WEISE, Assistant Examiner US. Cl. X.R.

